Recently, stirling engines with good theoretical efficiency have been increasingly focused on, and its purpose is to recover exhaust heat of internal combustions provided in vehicles such as automobiles, buses, or trucks, or exhaust heat of factories. High thermal efficiency of the stirling engine is expected. Further, the stirling engine can use low-temperature difference alternative energies such as solar heat, geothermal heat, or exhaust heat, because the stirling engine is an external combustion which heats the working fluid from its outside. The stirling engine has an advantage of saving energy. In a case where the stirling engine recovers the exhaust heat of an internal combustion or the like, it is necessary to reduce the friction of sliding portions as much as possible and to improve the efficiency of recovery of the exhaust heat. In contrast, Patent Documents 1 and 2 disclose stirling engines, where friction between a piston and a cylinder is reduced by the provision of a gas bearing therebetween, and where the piston is supported by an approximate straight-line mechanism using a grasshopper mechanism.
Moreover, Patent Documents 3 to 6, considered relative to the present invention, disclose a piston provided with a resin. The techniques disclosed in Patent Documents 3 to 5 are the provision of a resin to reduce the friction between the cylinder and the piston which slidably come into contact with each other. The technique disclosed in Patent Document 6 discloses the provision of a resin functioning as a buffer material.